Can I substitute gherkins for pickles in a potato salad?
Absolutely yes, but bear in mind they are sweet.
I do it all the time. Gives, as Tiggy points out, a hint of sweetness.
Let me echo tiggybee's "absolutely yes". In fact I would prefer them in a potato salad.
Gherkin actually refers to the type of cucumber used to make pickled gherkins. They come either sweet or dill commercially. So, if you would like to substitute dill pickles for dill gherkins then yes, if you want to substitute sweet gherkins for dill pickles then one would have to decide if they wanted the sweet flavor over the dill. But, I don't even add pickles to my potato salad. I hope this helps!
If you like a pickle straight out of the jar you will like it in your potato salad. I've been known to use chopped sweet gherkins, chopped bread and butter, chopped kosher dills, and pretty much any kind of pickle that comes to hand.
I love pickles out of the jar but hate em on everything else so I put capers in my potato salad. Just a suggestion.